The present invention relates to an image forming apparatus, such as an electrophotographic copier, facsimile machine, or printer, or combinations thereof.
In recent years, along with performance enhancement of image forming apparatuses such as digital copiers, comprehensive digital devices having not only a copying function, but also a printer function have been developed and widely used.
In such a digital copier or the like, cleaners are used in a method for collecting residue toner material occurring on a photoreceptor surface. A cleanerless process is known as being advantageous to implement, for example, apparatus miniaturization and toner saving. Nevertheless, however, although no cleaners are provided in the photoreceptor, cleaners for cleaning a transfer belt, an intermediate transfer member, and a like are necessary in a color digital copier, printer, or the like having a tandem configuration. In this connection, a toner collection method has been disclosed. According to the method, toner deposited on media such as a transfer belt and an intermediate transfer member is not cleaned by a dedicated cleaner therefor, but residue toner material is tentatively returned to the side of photoreceptors, whereby to collect the residue toner.
For example, Jpn. Pat. Appln. KOKAI Publication No. 2003-295542 discloses toner collection methods by way of examples. In one example method, patterns of individual colors intentionally printed on a transfer belt to perform image quality control are serially selectively returned to photoreceptors of corresponding colors and are then collected by developing units of the individual colors. In another example, when an image is inadvertently printed on the belt because of, for example, a paper jam, while in the case of a monochrome pattern, the pattern is returned to a photoreceptor in a station of the corresponding color, whereas in the case of mixed color patterns of two or more colors, the patterns are collectively returned to a photoreceptor in a black-color station, and the patterns are then collected by the black-color developing unit in which the mixed color is inconspicuous. According to the above-described conventional techniques, the amount of toner to be collected and reused in, for example, a direct transfer method, so that even when a paper jam has occurred, the amount of other-color toner being entrained into the black-color developing unit is small.
However, when the method for collecting toner material into the developing unit is used in an image forming apparatus using an intermediate transfer method, a problem is generated in which a large amount of other-color toner as being a secondary-transfer residue toner is entrained into the black-color developing unit, thereby changing the color property of black.